1. Field of the Invention
The present invention relates to the processing of semiconductor wafers or similar items, and more specifically, to the drying of semiconductor wafers after fluid treatment.
2. Description of Related Art
The production of semiconductors commonly involves several process steps in which wafers are submerged in fluids. For instance, wafers generally undergo etching and cleansing steps during fabrication. Such processes generally are performed in fluid baths (e.g., baths of etching solutions or cleaning solutions) that are applied to the wafers in a tank, or into which the wafers are dipped. Although many techniques are employed to keep contaminants out of the fluid baths and to remove particulates from the baths, particulate contaminants in the baths continue to be a problem.
Through surface tension and other forces, such particles are easily transferred to the wafer surface when withdrawing the wafers from the fluid baths or draining the fluid from the tank. Particles deposited onto the wafer surface contaminate the wafer and detrimentally affect the electrical proficiency of the microscopic electrical circuitry on the wafer surface. This is especially true as integrated circuits became smaller and the size and number of such particles becomes more critical.
During conventional wafer fabrication, wafers are dried following fluid processing. Prior drying processes have involved a variety of different techniques including, for example, centrifugal drying (i.e., spin drying), evaporation drying and chemical drying. U.S. Pat. Nos. 4,079,522, 4,902,350, 5,071,488 and 5,090,432 disclose examples of prior evaporation drying methods. U.S. Pat. Nos. 4,991,761 and 4,984,597 disclose examples of prior chemical drying methods.
Prior drying processes suffer from a number of drawbacks. For example, evaporation drying tends to leave streaks and spots of residue from the processing fluids and other contaminants on the wafer surface as the wafer emerges from the process fluid. Centrifugal drying subjects the wafers to mechanical stresses and tends to produce static charges on the wafer surfaces which attract air borne contaminants. Prior chemical drying methods usually consume large volumes of chemicals (which increases production costs) and produce large volumes of chemical waste. The produced chemical waste poses safety and disposal concerns. And, in general, prior drying processes fail to produce ultra-clean wafers with minimal levels of particle contaminants and chemical residue (i.e., contaminant levels below 0.003 particles/CM.sup.2 of 0.2 microns or greater).